1. Field of the Invention
The present invention relates to a cooling drum used in a twin-drum continuous casting machine.
2. Description of the Related Art
As shown in FIGS. 21(a) and 21(b), a well-known, conventional twin-drum continuous casting machine, for example, has a moving mold formed by a pair of rotating cooling drums 1a, 1b and a pair of side dams 2, 2 abutting on opposite end portions (faces) of the drums. Molten steel 6 is supplied from a tundish 4 into the moving mold 3 through a nozzle 5. A molten pool 3p of a prescribed level is formed in the moving mold 3 while the molten steel is simultaneously cooled by the pair of drums 1a, 1b to progressively form solidified shells 6s, 6sxe2x80x2. The solidified shells 6s, 6sxe2x80x2 are forced together and integrated at the gap portion formed at the most proximate points of the cooling drums 1a, 1b, thereby continuously casting a slab 6c. The drum end portions are generally given a projecting shape for sealing in the molten steel.
In order to ensure formation of excellent shells 6s, 6sxe2x80x2 by promoting cooling of the molten steel 6 at the outer peripheral surfaces of the cooling drums 1a, 1b used in this twin-drum continuous casting machine, the cooling drums 1a, 1b are generally made of copper or a copper alloy with good thermal conductivity. They are also equipped with internal cooling structures 7 and shaft 1s so as make them resistant to thermal load.
As shown in FIGS. 21(a) and 21(b), each of the end portions of the cooling drums is formed with an end portion 1t. The end surfaces of the end portions 1t press against the side dams 2, 2 and are worn as they slide thereon during rotation. Irregular gaps are apt to arise between the end portions 1t and the side dams 2, particularly when the side dams 2 experience vibration or thermal deformation. The molten steel invades and solidifies in these gaps to make the sliding surfaces rough. This abruptly degrades the molten steel sealing performance of the sliding surfaces and spoils the shape of the slab edge portion. It also deforms the shapes of the end portions 1t and the side dams 2, further aggravating wear and shortening their service life. This makes it impossible to realize stable continuous casting operation over a long period.
For overcoming this problem, JP-A-(unexamined published Japanese patent application) 6-335751, for example, discloses a technique of coating the end portions (faces) of the cooling drums with surface layers exhibiting high-strength, wear resistance and lubricity, e.g., layers composed of Coxe2x80x94Crxe2x80x94Alxe2x80x94Y-system alloy, tungsten carbide (WC) or the like. However, this alone does not curb the deformation and wear occurring at the cooling drum end portions to an extent that readily enables stable continuous casting operation.
An object of the present invention is to provide a cooling drum for a twin-drum continuous casting machine that is capable of ensuring an excellent drum body interior cooling effect and advantageously overcoming both the problem of wear of the cooling drum end portions that are pressure-contacted with, and slide on, the side dams and the problem of their local deformation, and that, as a result, can ensure long-term maintenance of a suitable pressure-contact sliding state between the side dams and the cooling drum so as to enable stable continuous casting over a prolonged period.
In one of its aspects, the present invention provides:
(1) A cooling drum for a twin-drum continuous casting machine equipped with a pair of cooling drums that rotate in opposite directions and a pair of side dams that abut on opposite end faces of the cooling drums to define a moving mold, the cooling drum comprising a drum body portion formed of a material having high thermal conductivity and end portions formed of a material having higher hardness than the material of the body portion.
In another of its aspects, the present invention provides:
(2) A cooling drum for a twin-drum continuous casting machine equipped with a pair of cooling drums that rotate in opposite directions and a pair of side dams in pressure-contact with opposite end faces of the cooling drums, the cooling drum comprising a drum body portion of a material having a thermal conductivity of 100-400 W/mK and drum end portions part or all of whose portions in pressure-contact with the side dams and/or part or all of whose inner regions are formed of a reinforcing material that is a high-hardness material having a Vickers hardness: Hv (250 g) of 300-600.
In another of its aspects, the present invention provides:
(3) A cooling drum for a twin-drum continuous casting machine according to (1) above, wherein the drum body portion is formed of copper or a copper alloy.
In another of its aspects, the present invention provides:
(4) A cooling drum for a twin-drum continuous casting machine according to (1) above, wherein the high-hardness material forming the end portions is material of the body portion which has been subjected to a nitriding or a carbonizing high-hardness treatment.
In another of its aspects, the present invention provides:
(5) A cooling drum for a twin-drum continuous casting machine according to (1) above, wherein the high-hardness material forming the end portions is material of the body portion welded to a cladding material.
In another of its aspects, the present invention provides:
(6) A cooling drum for a twin-drum continuous casting machine according to (1) above, wherein the high-hardness material of the end portions is coated with a super high hardness material to a thickness of 10-500 xcexcm by flame spraying or plating.
In another of its aspects, the present invention provides:
(7) A cooling drum for a twin-drum continuous casting machine according to (1) above, wherein an outer peripheral surface of the drum body portion or an outer peripheral surface of the drum body portion and outer peripheral surfaces of the end portions are coated with heat conducting layers having a thermal conductivity of not less than 30 W/mK and a thickness of 10-5000 xcexcm by flame spraying or plating.
In another of its aspects, the present invention provides:
(8) A cooling drum for a twin-drum continuous casting machine according to (2) above, wherein the ratio of the coefficient of thermal expansion of the reinforcing material to that of the drum body portion material is 0.5 to 1.2.
In another of its aspects, the present invention provides:
(9) A cooling drum for a twin-drum continuous casting machine according to (2) above, wherein the reinforcing material is formed of one or more of stainless steel, high-Mn cast steel, Nixe2x80x94Crxe2x80x94Mo steel and Inconel.
In another of its aspects, the present invention provides:
(10) A cooling drum for a twin-drum continuous casting machine according to (2) above, wherein the reinforcing material formed at the inner regions of the drum end portions is detachably fastened mechanically to the drum body portion material.
In another of its aspects, the present invention provides:
(11) A cooling drum for a twin-drum continuous casting machine according to (2) above, wherein the reinforcing material formed at the drum end portions is joined to the drum body portion material directly or through an intervening plating layer.
In another of its aspects, the present invention provides:
(12) A cooling drum for a twin-drum continuous casting machine according to (2) above, wherein the reinforcing material formed at the drum end portions is integrated with a cladding material that is joined to the drum body portion material and is composed of a material similar to the drum body portion material.
In another of its aspects, the present invention provides:
(13) A cooling drum for a twin-drum continuous casting machine according to (2) above, wherein the reinforcing material formed at the drum end portions is coated on the drum body portion material directly or through an intervening plating layer by weld-overlaying or flame spraying.
In another of its aspects, the present invention provides:
(14) A cooling drum for a twin-drum continuous casting machine according to (11) above, wherein the reinforcing material formed at the drum end portions is supported by reinforcing material provided at the inner regions of the drum end portions.
In another of its aspects, the present invention provides:
(15) A cooling drum for a twin-drum continuous casting machine according to (2) above, wherein the reinforcing material formed at the drum end portions and the reinforcing material formed at the inner regions of the end portions are integrally formed, the reinforcing material formed at the drum end portions is welded to the drum body portion material through an intervening plating layer, and the reinforcing material formed at the inner regions of the drum end portions is detachably fastened mechanically to the drum body portion material.
In another of its aspects, the present invention provides:
(16) A cooling drum for a twin-drum continuous casting machine according to (2) above, wherein the reinforcing material formed at the inner regions of the drum end portions is segmented in the circumferential direction or radial direction.
In another of its aspects, the present invention provides:
(17) A cooling drum for a twin-drum continuous casting machine according to (1) above, wherein at least outermost surface layers of the drum end portions that are pressure-contacted with and slide on the side dams are coated with super-high hardness material layers of a thickness of 10-500 xcexcm and a Vickers hardness: Hv (250 g) of 600-1000 by flame spraying or plating.
In another of its aspects, the present invention provides:
(18) A cooling drum for a twin-drum continuous casting machine according to (2) above, wherein the reinforcing material is provided with a cooling structure.
In another of its aspects, the present invention provides:
(19) A cooling drum for a twin-drum continuous casting machine according to (18) above, wherein the cooling structure of the reinforcing material is one or a combination of two or more of a heat pipe, a water-cooling structure and an effusion cooling structure.